Taxonomy of Echinostoma revolutum and 37-Collar-Spined Echinostoma spp.: A Historical Review

Abstract

Echinostoma flukes armed with 37 collar spines on their head collar are called as 37-collar-spined Echinostoma spp. (group) or 'Echinostoma revolutum group'. At least 56 nominal species have been described in this group. However, many of them were morphologically close to and difficult to distinguish from the other, thus synonymized with the others. However, some of the synonymies were disagreed by other researchers, and taxonomic debates have been continued. Fortunately, recent development of molecular techniques, in particular, sequencing of the mitochondrial (nad1 and cox1) and nuclear genes (ITS region; ITS1-5.8S-ITS2), has enabled us to obtain highly useful data on phylogenetic relationships of these 37-collar-spined Echinostoma spp. Thus, 16 different species are currently acknowledged to be valid worldwide, which include E. revolutum, E. bolschewense, E. caproni, E. cinetorchis, E. deserticum, E. lindoense, E. luisreyi, E. mekongi, E. miyagawai, E. nasincovae, E. novaezealandense, E. paraensei, E. paraulum, E. robustum, E. trivolvis, and Echinostoma sp. IG of Georgieva et al., 2013. The validity of the other 10 species is retained until further evaluation, including molecular analyses; E. acuticauda, E. barbosai, E. chloephagae, E. echinatum, E. jurini, E. nudicaudatum, E. parvocirrus, E. pinnicaudatum, E. ralli, and E. rodriguesi. In this review, the history of discovery and taxonomic debates on these 26 valid or validity-retained species are briefly reviewed.

Keywords: 37-collar-spined echinostome; Echinostoma; Echinostoma revolutum; historical review; ‘revolutum’ group.

Fig. 1

A phylogenetic tree of Echinostoma revolutum (Southeast Asian and American lineages) and 6 other 37-collar-spined Echinostoma group constructed based on 184 bp of mitochondrial cox1 sequences by maximum-likelihood method using the MEGA-X program employing Tamura-nei model of nucleotide substitution with 1,000 bootstrap replications. Opisthorchis viverrini was used as an outgroup.

Fig. 2

A phylogenetic tree of Echinostoma revolutum (Eurasian and American lineages) and 13 other 37-collar-spined Echinostoma spp. constructed based on 472 bp of mitochondrial nad1 sequences by maximum-likelihood method using the MEGA-X program employing Tamura-nei model of nucleotide substitution with 1,000 bootstrap replications. O. viverrini was used as an outgroup.

Fig. 3

Adult specimens of Echinostoma revolutum (A) from Thailand (courtesy of Prof. Chalobol Wongsawad, Chiang Mai University), E. cinetorchis (B) from South Korea, E. mekongi (C) from Cambodia, and E. robustum (D) from India under the same magnification. Scale bar=2 mm.